Semiconductor devices have been prepared in the past using various combinations of metallization processes for rerouting connections to the circuit contact pads. They generally consist of first depositing thin layers of metal and later removing those portions which are not needed for the desired network. This add-and-subtract method is generally costly and involves hazardous materials and often chemical waste; it also tends to lower the process yield due to repeated handling of the chips, and may also generate stress in the chips themselves. The feature sizes achievable for rerouting remain severely limited, and the choice of metals which can be processed is restricted. When insulating layers have to be deposited, existing technology requires extra care for protecting those parts of the chip, which should not receive any deposition, such as the circuit contact pads, amounting to a cumbersome and time consuming deposition process. On the other hand, commercial and military systems urgently require flexible, cost-effective methods for mass producing rerouted semiconductors chips which are compatible with the increasing demands for more signal input/outputs and power handling, and are able to hold pace with quickly changing design rules and feature sizes.
Techniques have been investigated to use laser energy for direct deposition of metals and other solids from the gas phase. The incident laser energy causes photodecomposition or photolysis of the metal-containing component in the gaseous phase. Selective heating of substrate areas definded by incident focussed laser beams has been used to initiate reactions of gaseous precursors, resulting in the deposition of the desired solid reation product. The studies investigated not only the composition of the gases and the properties of different lasers, but also the effect of inorganic and organic substrates, adhesion, the possible need of seeding before deposition, and the required temperatures. Most of these investigations have been for research or specialty product development purposes. For example, the local deposition of aluminum and silicon nitride has been descibed in U.S. Pat. No. 4,340,617, July 1982, Deutsch et al.; deposition of palladium in U.S. Pat. No. 4,574,095, March 1986, Baum et al.; deposition of silicon dioxide, tungsten, molybdenum and titanium in U.S. Pat. No. 4,699,801, October 1987, Ito et al . . . The deposition of gold has been investigated by T. H. Baum in "Laser Chemical Vapor Deposition of Gold", J. Electrochem.Soc. vol. 134, pp, 2616-2619, 1987; the deposition of copper by F. A. Houle, et al, in "Laser Chemical Vapor Deposition of Copper", Appl. Phys. Lett. vo. 46, pp. 204-206, 1985; by J. Han et al., in "Combined Experimental and Modeling Studies of Laser-assisted Chemical Vapor Deposition of Copper . . . ", J. Appl. Phys. vol 75 (4), pp. 2240-2250, 1994; the deposition of tungsten and copper lines has been described by R. F. Miracky in "Laser Advance into Microelectronics Packaging", Laser Focus World vol. 27, pp.85-98, 1991.
It has been demonstrated that achievable laser focus is compatible with the feature sizes in semiconductor assembly and packaging (10 to 20 .mu.m), and that the cost of laser application is lower than comparable mature mechanical machines. The goal, however, of offering for the commercial and military markets cost-effective, reliable, rerouted semiconductor products, manufacured in high volume and with flexible, low-cost production methods, has remained elusive, until now.